JPH07242955A - Treatment method for reuse of dust generated in steelmaking furnace as raw material for steelmaking - Google Patents

Abstract

(57) [Abstract] [Purpose] The dust generated by steelmaking furnaces containing iron oxides, non-ferrous metals, etc. is treated in a steelmaking furnace so that it can be used as an iron source. [Structure] Dust generated from a steelmaking furnace is supplied with a gas containing 10 to 100% of hydrogen in an externally heated rotary furnace to reduce 70 to 100% of iron content and to exist in a charging raw material. 50% or more and less than 80% of the zinc content is separated by reduction / evaporation, and the treated dust thus obtained is reused as a steelmaking raw material. When the chlorine concentration is high, the chlorine content is reduced to 1.0% or less by washing with water before heating, and then the above operation is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating dust generated in a steelmaking furnace that causes various problems when it is reused as a raw material for ironmaking in a steelmaking furnace in a usual manner so that it can be used as a steelmaking material.

[0002]

2. Description of the Related Art Dust generated from a steelmaking furnace mainly consists of iron, but most of iron is iron oxide.
Further, depending on the raw material conditions of the steelmaking furnace, dust contains a card element such as zinc or lead that easily evaporates. This dust is currently processed outside the steel mill to recover zinc, but the commonly used carbon reduction method requires high temperatures for processing, so iron reoxidation in the furnace is required. Is likely to occur, and the residue is not suitable for use as an iron source in a steelmaking furnace, and is not effectively used. This is because, when dust mainly consisting of iron oxide is recycled to the steelmaking furnace, energy for reducing the iron oxide content is required, which hinders the productivity of the melting furnace.

In order to meet demands from the viewpoint of resources and environment in the future, nonferrous metal components are recovered from steelmaking dust under energy efficient conditions, and iron components are also easy to use in steelmaking furnaces. It needs to be reused as a source. From such a viewpoint, there is known a method for removing zinc by reducing steelmaking dust with hydrogen. However, if 90% or more of zinc is to be removed, the basic unit of the reducing agent becomes high, which increases the processing cost. There is a problem that the container is easily corroded during hydrogen reduction when the steelmaking dust contains chlorine.

[0004]

In view of the above circumstances, the present invention provides a method for treating steelmaking dust under proper conditions so that the dust can be economically used as an iron source in a steelmaking furnace. That is the purpose.

[0005]

In order to achieve such an object, the inventors of the present invention have studied various methods for efficiently treating dust generated in a steelmaking furnace to provide an iron source that is easy to use in the steelmaking furnace. Thus, the present invention has been completed. That is, the gist of the present invention is as follows.

(1) The dust generated from the steelmaking furnace is charged into an externally heated heating furnace to contain hydrogen in an amount of 10 to 100% by volume.
The contained gas is supplied to reduce 70% to 100% by weight of iron, and the amount of zinc contained in the charging raw material is reduced to 5%.
A processing method for reusing the dust generated by a steelmaking furnace as a raw material for steelmaking, characterized by separating 0 wt% or more and less than 80 wt% by reduction / evaporation.

(2) Continuing from the first step of removing the dust generated from the steelmaking furnace by washing with water to a chlorine content of 1.0 wt% or less, 10% of hydrogen is discharged in an externally heated heating furnace.
70% iron content by supplying gas containing 100 vol%
100 wt% is reduced, and the second step of separating 50 wt% or more and less than 80 wt% of the zinc content existing in the charging raw material by reduction / evaporation is used to recycle the steelmaking furnace generated dust as a steelmaking raw material. The processing method to use.

[0008]

The present invention will be described in detail below by taking as an example a method in which dust generated from an electric furnace is used as a raw material and treated to be used as a steelmaking raw material in the electric furnace. The dust generated from the electric furnace is usually 3 to 5 wt%
Contains chlorine. Dust separated from the exhaust gas by a conventional method, for example, a bag filter is first washed with water to reduce the chlorine content. In order to facilitate this operation, it is desirable that the dust be lumped in advance by briquetting. Chlorine content is mainly contained in the dust as sodium chloride, potassium chloride, and calcium chloride, but chlorine content in the dust can be reduced by eluting them with water. If the reduction treatment of the present invention is performed while the dust contains a large amount of chlorine, the corrosion of the container due to chlorine is likely to occur. Therefore, when the test was conducted by reducing the chlorine concentration to various levels, it was found that the adverse effect of chlorine can be suppressed to an acceptable level by setting the chlorine concentration to 1.0% or less. If the dust originally does not contain chlorine in excess of 1.0 wt%, this step can be omitted.

In the second step of the present invention, the dust treated as described above is charged into a heating furnace which is externally heated, and a gas containing 10 to 100 vol% or more of hydrogen is caused to flow to 70 to 100 wt% of iron. % Reduction and at the same time 50w zinc content
Reduce, evaporate, and separate t% or more and less than 80 wt%. This heating furnace may be directly connected to the steelmaking dust processing line, or may be a separate device cut off. Although various types of heating furnaces can be adopted, a rotary furnace which is easy to perform uniform heating will be described below as an example.

The rotary furnace is made of cast metal, and the outside is heated by gas. When the temperature of the heated dust exceeds 950 ° C., the heat load on the container becomes too large and the life of the container becomes short. Therefore, the temperature range of 700 to 950 ° C. is usually selected as the heating temperature of the dust. In this case, there is a relationship as shown in FIG. 1 between the reduction rate of iron and the removal rate of zinc. In the processing step of the present invention,
It is necessary for zinc to be removed by 50% or more for use as a steelmaking raw material in a steelmaking furnace. Because, if the zinc removal rate is less than 50% and the dust is recycled, the zinc concentration in the electric furnace system becomes high, and the refractories of the electric furnace and the electric system are likely to cause troubles. Because it will be. In this case, the lead content is 90 wt%
Since the above is eliminated, the problems due to the circulation of lead can be prevented.

As can be seen from FIG. 1, the zinc removal rate is 5
To achieve 0 wt% or more, the reduction rate of iron is 70 wt%
It is necessary to be above. In order to realize this in the stable operating temperature range of the external heating rotary furnace, the hydrogen concentration in the reducing gas to be supplied needs to be 10 vol% or more. Further, although the reduction rate of iron can be increased to 100 wt%, there is no problem in the present invention, but conditions such as required temperature and time become sharply strict, so 90% or less is preferable.

On the other hand, there is a relationship as shown in FIG. 2 between the removal rate of zinc and the amount of hydrogen gas required for removing a unit amount of zinc. From Figure 2, if the removal rate of zinc is 80wt%
It can be seen that the required amount of hydrogen gas used increases sharply if the above is attempted. For the purpose of the present invention, there is no problem even if the hydrogen concentration of the supplied gas is increased to 100 vol%.

If the iron in the dust is not used in the steelmaking furnace, it is necessary to strengthen the reducing conditions in order to sufficiently reduce the non-ferrous metal components such as zinc and lead in the dust. Since the dust after separating a predetermined amount of non-ferrous metal is used as a steelmaking raw material, the most energetically favorable condition can be selected within a range satisfying the condition.

In the present invention, the gas generated from this reduction step is cooled to 350 ° C. to separate non-ferrous metals such as zinc and lead, and then dust is removed with a bag filter at a temperature of 120 ° C. or higher. After removing the water by lowering the temperature to 70 ° C. or lower, it is used as a fuel for external heat in the reduction step. If the amount of generated gas is larger than the amount required for this external heat, equipment such as a tank is required to use the gas in other steps, which is not economical. Therefore, in the present invention, the generated gas is in a state equal to or less than the energy required for the external heat so that the generated energy does not become excessive. For that purpose, it is effective to reduce the separation rate of zinc by reduction / evaporation to less than 80% as a whole. In this state, reoxidation of iron after reduction can also be suppressed to a low level, so that energy consumption as a whole can be reduced.

After completion of the above-mentioned treatment, those mainly composed of iron are sealed with an inert gas in order to suppress reoxidation and, if necessary, molded into a briquette or the like and then used as an iron raw material in a steelmaking furnace. Charge.

[0016]

【Example】

(Example 1) A heating furnace for reducing dust is composed of a cast iron inner cylinder (1 mφ ×) inside an outer cylinder whose inner surface is lined with a refractory material.
5 mL) was used and this was rotated at 1 rpm. Combustion heating is performed between the inner cylinder and the outer cylinder by using the gas generated in the reduction step of the present invention as fuel. The temperature is
The heated product in the inner cylinder was measured with a pyrometer.

The dust components before treatment are shown in Table 1. Since this dust has a low chlorine concentration, it was directly molded into a briquette and continuously inserted into the heating furnace and discharged.

[0018]

[Table 1]

The heat treatment conditions are as follows. Supply gas in the furnace: vol%, hydrogen: 45%, CO: 24
%, CO _2: 5%, nitrogen: the maximum heating temperature of the 25% dust: 870 ° C. oven residence time: 55 min gas consumption: 130 Nm ³ / raw material dust -t This process iron-reducing ratio 90 wt% of the dust, A zinc removal rate of 66 wt% and a lead removal rate of 98 wt% were obtained. The treated dust was reused in an electric furnace in a state of a reoxidation rate of 8 wt% while preventing oxidation in a nitrogen atmosphere. No particular problems were found in the electric furnace operation.

The gas after separation of the non-ferrous metal was used in total for external heat. (Example 2) Table 2 shows the dust components before the treatment. Since this dust has a high chlorine concentration, it was dechlorinated. The dechlorination treatment is a method in which dust is briquetted and water is poured, but the chlorine content can be reduced to 0.6%. This was continuously charged into and discharged from the heating furnace for reduction. The heating furnace used for dust reduction is the same as in Example 1.

[0021]

[Table 2]

The heat treatment conditions are as follows. Supply gas in the furnace: vol%, hydrogen: 45%, CO: 24
%, CO ₂ : 5%, nitrogen: 25% Maximum dust heating temperature: 850 ° C. Furnace residence time: 59 minutes Gas usage: 145 Nm ³ / Raw material dust-t By this treatment, the iron reduction rate of dust is 87 wt%, A zinc removal rate of 63 wt% and a lead removal rate of 96 wt% were obtained. The treated dust was reused in an electric furnace in a state of a reoxidation rate of 7 wt% while preventing oxidation in a nitrogen atmosphere. No particular problems were found in the electric furnace operation.

The gas after separation of the non-ferrous metal was used entirely for external heat. In addition, when this raw material was used, the life of the container was five times as long as that of the case where the treatment was performed without removing chlorine.

[0024]

Industrial Applicability According to the present invention, the steelmaking furnace dust can be recycled and used economically, and the effect is great in terms of resources and environment.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a reduction rate of iron in dust and a removal rate of zinc by reduction / evaporation.

FIG. 2 is a diagram showing a relationship between a zinc removal rate of dust and a required hydrogen gas amount for removing a zinc unit amount.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiichi Otani 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd. Technology Development Headquarters (72) Inventor Kazuya Kodama 3007, Nakajima, Nakajima, Himeji, Hyogo Prefecture Address Sanyo Special Steel Co., Ltd. (72) Inventor Tadayoshi Shigezumi No. 3007, Nakajima character, Shikoma-ku, Himeji City, Hyogo Prefecture Sanyo Special Steel Co., Ltd.

Claims (2)

[Claims] 1. Dust generated from a steelmaking furnace is charged into an externally heated heating furnace, a gas containing 10 to 100 vol% of hydrogen is supplied to reduce 70 to 100 wt% of iron, and 50w of zinc content in the raw material
A processing method for reusing the dust generated in a steelmaking furnace as a steelmaking raw material, characterized in that t% or more and less than 80% by weight is separated by reduction / evaporation. 2. Continuing from the first step of removing the chlorine content to 1.0 wt% or less by washing the dust generated from the steelmaking furnace with water, 10 to 1 hydrogen is added in an externally heated heating furnace.
Supplying gas containing 00 vol% 70 to 10 iron
Reducing 0 wt% of the zinc content in the charging raw material and reducing the amount of 50 wt% or more and less than 80 wt% of the zinc content existing in the charging raw material by the second step, the dust generated in the steelmaking furnace is reused as a steelmaking raw material. The processing method to use.